How do I repeat a gradient color ramp?
You can use a Color Ramp node and a Modulo converter node to achieve this result. 

Set up your nodes like this:



And this is the result:



What you are doing is you are making the Color Ramp node tell what color, and then you are mapping it using the Mapping node, and repeating it with the Modulo node. This makes it fully editable, you can change the color ramp, and the resulting texture will repeat endlessly.